Back frame of chair



FIG. 1 is a front view of a back frame of chair showing my new design;

FIG. 2 is a right side view thereof;

FIG. 3 is a left side views thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a perspective view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The ornamental design for a back frame of chair, as shown and described.